Rock bolts, sometimes referred to as friction rock stabilizers, are support mechanisms designed to be placed into a drilled hole or opening in the roof, side, or bottom of an underground structure where such bolts are anchored and sometimes tensioned to support the overlying structure or external utilities, such as pipes or mesh. Rock bolts are commonly used in applications involving mining, rail, road and sewer tunnels, rail and road cut throughs, soil nails for hillside supports, hydro electric flumes, and karst zones. Rock bolts are commonly used in or around any structure which requires restraint through 360°, where rock or concrete exists as an anchoring medium. A typical type of such rock bolt is the Split Set® bolt which is sold by International Rollforms, Inc., Deptford, N.J. These bolts have two parts: a tube and a matching domed bearing plate. The tube may be slotted along its length. One tube end is tapered to facilitate insertion into a drill hole in the underground structure, and the other end has a welded ring flange to hold the bearing plate. With the bearing plate in place, the tube is driven into a slightly smaller drill hole to achieve an interference fit and thus hold the rock bolt in place. As the tube portion of the rock bolt slides into place, the full length of the slot narrows causing radial pressure to be exerted against the rock over its full contact length and also provides immediate plate load support.
Split Set rock bolts are typically manufactured by rolling or drawing a flat length of steel to create a circular profile along the length, leaving two ends open and forming an open split over the length. Then one end is cut and tapered over approximately 2 to 3 inches and welded shut while leaving the split open. Then an open-ended ring is welded at the opposite end to act as a retaining device for the bearing plates and assemblies. FIG. 1 is a front view of this type of rock bolt. As illustrated, matched bearing plate 1 and welded-on retaining ring 2 are associated with split hollow tube 3 to form rock bolt 4. Split Set rock bolts are manufactured by International Rollforms, Inc., Deptford, N.J.
Other types of conventional rock bolts include point anchor roof bolts, point anchor resin roof bolts and Swellex™ bolts.
A problem has existed regarding the use of the above-described Split Set, point anchor, point anchor resin, and Swellex rock bolts. After placing the rock bolts in service in the roof or wall rock of the underground structure, water contained in fissures in the rock leaks into the rock bolt and drains through the rock bolt onto the floor of the underground structure. Such drainage results in undesirable wet conditions and can result in corrosion of the rock bolt, the need for pumping accumulated water, increased maintenance of pumps and lines, the need to treat water prior to discharge as well the creation of safety issues. This long standing problem in the art has not been satisfactorily addressed to date. The present invention is believed to address and solve such long standing problem in the art by providing a novel technique and system, rock bolt assembly, and kit for preventing such water leakage. The present invention involves the use of a water-dissolvable sealing unit containing a water-activated expandable hydrophobic pre-polymeric resin. Such sealing unit is contained within the rock bolt and functions to provide a seal against water leakage. Once the rock bolt assembly is in place in an underground structure and is contacted with water, the water dissolvable portion or outer surface of the sealing unit becomes dissolved by the water, which in turn permits the water-activated expandable hydrophobic pre-polymeric resin to react with water and seal both the annular space of the rock bolt assembly and any fissures present in the rock against water leakage. The invention of the present invention may be advantageously utilized in any rock bolt where annular space exists to minimize or seal against water leakage. In the context of the present invention, annular space means the space or open area from the inner diameter of the drilled or pre-formed hole to the outer diameter of the Split Set bolt and at the top, where the sealing unit is located, to the top of the hole.
Other types of rock bolts, in addition to those described above, are known in the art and include those shown in U.S. Patent Publication No. 20040161316 and U.S. Pat. Nos. 4,537,535; 5,249,898; 5,387,060; 6,135,674; 7,073,981; and 7,338,234. The above patent publication and patents do not contain a water-dissolvable sealing unit which contains a water-activated expandable hydrophobic pre-polymeric resin and thus do not function in the above described manner to create a seal against water leakage.